Undersignature is a term that is commonly used to refer to a signature that is placed beneath or below the main signature on a document. However, there are several synonyms for this term that can be used interchangeably, depending on the context of the situation. Some of the most commonly used synonyms for undersignature include counter-signature, co-signature, additional signature, second signature, and twin signature. These terms can be particularly useful in legal documents where multiple parties may need to sign in order to formalize a contract or agreement. Regardless of the term used, the purpose of the undersignature is to indicate that the person has read and agreed to the contents of the document.